The present invention relates generally to non-positive displacement fluid pumps, and more particularly to submersible sewage pumps.
Submersible sewage pumps are generally located at the bottom of a septic tank or other receptacle in which sewage comprising mostly water and occasional solids is received. Such pumps generally operate intermittently under automatic control, such as by float actuated switches or other water level sensors. The intake of the pump is usually located quite near the floor of the septic tank, since it is desirable to pump out the sewage down to the lowest level possible. Unfortunately, the solids content of the sewage is also predominantly located near the floor of the septic tank and the pump intake. The pump is therefore susceptible to blockage or damage if solids that are too large should enter the pump intake. For this reason, measures to screen out oversized solids are desirable. One way of preventing the entry of oversized solids is to place the inlet aperture of the pump on the underside of the pump volute, and then support the volute above the floor of the septic tank on legs that are short enough to preclude passage underneath the volute of solids too large to pass safely through the pump inlet. Since sewage pumps are sometimes offered by the manufacturer in a range of solids pumping capacities to suit the application, in the past it has been necessary to manufacture a different volute for each size pump in order to incorporate variations in the size of the inlet aperture and a corresponding change in the length of the support legs to screen out solids larger than a selected maximum size. It would be desirable and advantageous with respect to cost to provide a range of pumps of different solids pumping capacities that all use a single common volute part. The present invention provides this desirable advantage.
In the past, the housings of sewage pumps have often been made of cast iron which is relatively durable and somewhat resistant to the corrosive effects of constant exposure to sewage. Nevertheless, cast iron can be corroded to an undesirable extent by sewage, which can lead to failure of the pump or, at the very least, make difficult the disassembly of the pump for maintenance or repair. Cast iron is also heavy and increases the cost of transportation of the manufactured pumps, and makes the pumps somewhat unwieldy to handle, especially in the larger sizes. Consequently, some manufacturers have attempted to replace some of the parts of their sewage pumps that were formerly cast iron with parts made of plastic. Suitable plastics are lighter than cast iron and less susceptible to chemical attack by corrosive sewage. Since plastic is less conductive of heat than cast iron, however, it has heretofore been the practice to leave at least one of the major external components of the pump housing, such as the volute, constructed of cast iron in order to provided a path for heat to be conducted from the encased electric motor to the sewage water. It would be desirable and advantageous to construct the entire externally exposed portion of the pump of plastic in order to reduce weight and present a non-corrodible exterior, while maintaining sufficient cooling of the electric motor. The present invention provides this desirable advantage.
Sewage pumps are sometimes provided with a threaded outlet to facilitate the connection of a waste pipe to the pump to carry away the effluent. In the past, with the outlet formed of cast iron, the threads have been placed on the inside of the outlet or on the outside, but not on both the inside and the outside. It would be difficult to thread a cast iron outlet on both the inside and outside and maintain a desirable limit on the difference between the inside and outside diameters. Generally, cast iron would require an undesirably great wall thickness. Thus, the sewage pumps as manufactured in the past have fit only a single size of threaded pipe. In field installations, it is sometimes preferable to be presented with a choice of pipe sizes that can be used for connection to the pump outlet. It would be desirable and advantageous to provide a sewage pump that permits connection of its outlet to either one of two pipe sizes. The present invention provides this desirable advantage.